The present invention relates to a method and apparatus for inserting coils in the slots of a stator, and in particular to protection of the slot liner cuffs during insertion.
The magnetic cores for stators are typically made of a stack of steel or iron laminations into which a central bore and a circular array of slots opening into the bore have been stamped or machined. The slots receive windings of insulated copper or aluminum wire, which have been prewound by any one of a number of prior art processes. One such process is known as the wind and shed technique wherein turns of wire are wound around a stepped coil form assembly by means of a flyer, and the coils are shed off the end of the form into a coil transfer and insertion device. The following U.S. patents, which are owned by the assignee of the present application, disclose exemplary prior art wind and shed apparatus: U.S. Pat. Nos. 3,514,837; 3,672,040; 3,672,027; 3,765,080; Re.29,007 and 3,579,818. These patents are expressly incorporated by reference into the present application.
As the coils are being wound, they drop into a transfer and insertion device, which comprises a plurality of fingers arranged circularly about a stripper element. The insertion device is inserted into the central bore of the stator with the fingers being positioned at the ends of the stator teeth so as to guide the coils as they are inserted into the slots. The stripper element is extended into and through the central bore of the stator carrying with it the prewound coils, which are pulled over one face of the stator and into the slots. After insertion of the wedges, the insertion device is retracted out of the stator. Injection apparatus which is typical of that in wide use throughout the industry is disclosed in U.S. Pat. Nos. 3,324,536; 3,151,638 and 3,722,063. These patents are expressly incorporated by reference in the present application.
Since the corners of the slots adjacent the faces of the magnet core are quite sharp and often have burrs thereon, it is customary to insert slot liners into the slots prior to insertion of the coils. The slot liners are typically made of Mylar, which serves to insulate the wire from the sidewalls of the slot. The slot liners protrude beyond the faces of the stator core, and these portions are normally doubled over to form a double thickness cuff. The folded over portions of the cuffs expand slightly so as to engage the faces of the core and prevent the cuffs from sliding into the slots. Additionally, the cuffs prevent the wire from scraping against the sharp corners of the slots during insertion of the coils, and prevent the end turns from touching the face of the core when they are pressed into place in the final stages of manufacture of the stator.
One problem which occurs during pressing of the end turns into tight bundles is that of breaking the cuffs when they are bent over and pressed against the face of the core by the end turns. In order to support the cuffs during the final pressing operation, the prior art has employed cuff supports, which swing downwardly or are moved inwardly, as by a slotted cam ring, against the cuffs so as to prevent the cuffs from being bent over or highly stressed. Such cuff supports are disclosed in U.S. Pat. Nos. 3,913,373; 2,980,157; and 3,593,405.
Breakage of the liner cuffs is also a problem during insertion of the coils, and it is this problem that the invention according to the present application solves. When there is a very high slot fill, which occurs when the number of turns and wire diameter is large and the slot size is relatively small, very high frictiinal forces are developed on the wire and on the cuffs of the slot liners during insertion. Typically, this occurs in connection with the larger coils of the main winding, for example, the three largest coils in a five coil main winding.
The coils are initially wound in a generally oval shape, and, because of the type of tooling typically used for insertion, the coils are pulled across the face of the stator core and then up into the slots. This means that the wire must make an abrupt 90.degree. bend or change in direction in order to travel in the axial direction up into the slots. The point at which this change of direction occurs coincides with the slot liner cuffs, which are disposed around the periphery of the slots. Thus, very high frictional and pressing forces are exerted on the slot liner cuffs as the wire is pulled over them, and this may easily result in breakage of the cuffs and the consequential exposure of the sharp edges of the slots to the wire as it is being pulled into the slots. This strips the insulation from the wires and permits the wires to remain in contact with the metal core thereby resulting in a short circuit. Furthermore, increased frictional forces result as the wire is drawn over the slot liner cuffs.
Some potential solutions to the problem of cuff breakage due to high frictional forces during insertion included reshaping the wedge guides so as to provide more available space within the slots during insertion, changing the shape of the winding form so as to change the shape of the prewound coils, and reducing the thickness of the wedge guides. None of these solutions have been satisfactory, however, and the problem of cuff breakage during insertion under high slot fill conditions has persisted.
Accordingly, it is an object of the present invention to provide improved methods and apparatus for inserting prewound coils in the slots of a stator core wherein breakage of the slot liner cuffs is minimized.
It is a further object of the present invention to provide a method and apparatus for inserting coils under high slot fill conditions wherein the coils are supported and guided over the slot liner cuffs in a manner such that high frictional and pressing forces, which would otherwise tend to severely deform and damage the cuffs, are avoided.
It is a further object of the present invention to provide a method and apparatus for inserting coils in stator slots wherein damage to the wires from scraping against the sharp corners of the stator slots is avoided.
A still further object of the present invention is to provide a method and apparatus for inserting coils wherein the frictional forces on the wire as it is being pulled into the slots is minimized.
Yet another object of the present invention is to provide a method and apparatus for protecting the slot liner cuffs during insertion which is capable of easy implementation into existing insertion machinery.